The Browser is the fundamental development tool in Squeak for reading ("browsing") and editing Smalltalk source code.

You can open a Browser in Squeak from the World menu by clicking on the "open..." submenu and then selecting "browser (b)".
The classic 5-paned Smalltalk "System Browser" looks like this in Squeak:

(The browser in this picture also has the optionalButtons and annotationPanes Preferences turned on. These are the two horizontal panes cutting across the middle of the browser... they can be very useful.)